I didn't check it a few days ago and during a ride within 100 yards she slowed, clattered, and seized up
To me, it sounds like most of the oil has been lost during the last two rides (80 miles?) but the question is where did all the oil go without being noticed?
Since the bike appears to be leak-free and no pool of oil was noticed on the floor after the last ride, I can only think of two possibilities, both related to the sump filling with oil whilst riding:-
- check the silencers for a black oily look inside and also the top of the pistons and cylinder head for black oily deposits.
- have a look at the breather pipe exit and the area around it, is there evidence of oil contamination?
If either of the above is true then it may suggest that the oil was burning off and blue smoke would have been seen in the exhaust. Oil may also have been spurting out of the breather.
Unless you had someone riding behind you, you would not be aware of the situation, until the engine seized.
I would check the scavenge side for any blockages which might cause the sump to fill.